(1) Field of the Invention
The present invention relates to a radiation-sensitive positive resist and a composition containing the same which are used in the production of LSI, VLSI or the like. Particularly, it relates to a radiation-sensitive positive resist and a composition containing the same which are favorably used in the production of photo masks by wet etching.
(2) Description of the Prior Art
PBS (poly-1-butenesulfone), "EBR-9" (poly-2,2,2-trifluoroethyl .alpha.-chloroacrylate: a product of Toray Industries, Inc.), PMMA (polymethyl methacrylate) and the like have been used as a radiation-sensitive positive resist.
Further, several copolymers of 2,2,2-trifluoroethyl .alpha.-chloroacrylate and other fluoroalkyl .alpha.-chloroacrylates have been proposed. For example, a copolymer comprising 2,2,2-trifluoroethyl .alpha.-chloroacrylate and heptafluorobutyl .alpha.-acrylate with a ratio of 60 to 40 is disclosed in Japanese Patent Publication No. 969/1982, while a copolymer comprising 2,2,2-trifluoroethyl .alpha.-chloroacrylate and 1,1-dimethylheptafluorobutyl .alpha.-chloroacrylate with a ratio of 60 to 40 is disclosed in U.S. Pat. No. 4,259,407.
Although PMMA has long been used as an electron beam-sensitive positive resist, it exhibits too poor a sensitivity to be used in the production of photo masks with an electron beam exposure system, thus being problematic in productivity.
PBS has been widely used in the production of photo masks. However, the sensitivity of PBS significantly varies depending upon development conditions such as temperature or humidity. Therefore, PBS exhibits so poor reproducibility that it is difficult to obtain photo masks in a high yield.
On the contrary, EBR-9 is free from the above disadvantages and exhibits excellent processing stability and reproducibility. However, it has a disadvantage of low sensitivity.
The above copolymers of 2,2,2-trifluoroethyl .alpha.-chloroacrylate with heptafluorobutyl .alpha.-chloroacrylate or the like could not also exhibit sufficiently high sensitivity, though the sensitivity thereof was enhanced to some extent.
The most suitable application of a radiation-sensitive positive resist is in the production of photo masks by wet etching. When the above copolymer of the prior art is applied on chromium blanks, subjected to pattern exposure with an electron beam exposure system and developed, the obtained resist pattern does not exhibit sufficient adhesion to chromium, so that the pattern tends to peel off, if the size thereof is less than 1.mu., and significant swelling of the resist pattern is observed.
Furthermore, when the polymer of the prior art is subjected to wet etching with an etchant, it is poor in adhesion to result in serious side etch.